Recently, in a mobile communication network, a multicast technology that multicasts data only to specified plural radio terminals has been focused upon. In a network that is called the Universal Mobile Telecommunication System (UMTS) of the 3rd Generation Partnership Project (3GPP) specification, a multicast technology that is called a Multimedia Broadcast and Multicast Service (MBMS) for providing a multimedia broadcast or a multicast service has been supported. Also in Long Term Evolution (LTE), prospects for supporting the MBMS have been investigated (Non-Patent Document 1). According to the 3GPP standard specification, it is possible to support the MBMS regardless of the kind of base station (for example, macro base station or micro base station).
The radio terminal can receive a multicast signal or a broadcast signal of MBMS data in any state of an idle state that is a standby state and an active state. Also, when the radio terminal moves to another cell while receiving the MBMS data, cell reselection, cell update, or handover is executed in conjunction with the communication state of the corresponding radio terminal. In an idle state, the radio terminal receives paging information using a paging channel (PCCH) from a serving radio base station, and confirms whether or not an incoming call is present based on the paging information. The cell reselection means an operation of changing a base station that transmits the paging information (i.e. current serving radio base station) to another base station (another serving radio base station). On the other hand, the radio terminal that is in an active state establishes synchronization with the serving base station and performs transmission-and-reception of user data. Handover is an operation in which the radio terminal in an active state changes the serving base station to another base station.
In the 3GPP specification UMTS or LTE, a femto base station (which is also called a home base station) is defined as an inexpensive small base station having a limited performance differently from a macro base station (see Non-Patent Document 2 and Non-Patent Document 3). A general femto base station is a small base station which is installed indoors, is connected to an existing broadband line, and performs communication by accessing a communication network of a cellular system, such as UMTS, LTE, or the like, through the broadband line.
Related art documents regarding the 3GPP are, for example, Non-Patent Document 1, Non-Patent Document 2, and Non-Patent Document 3 listed below.